Optical system

ABSTRACT

An optical system includes a first lens having negative refractive power and having two concave surfaces, a second lens having positive refractive power, a third lens having refractive power, a fourth lens having refractive power, a fifth lens having refractive power, a sixth lens having refractive power, and a seventh lens having refractive power. The first to seventh lenses are sequentially disposed from an object side.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/140,768 filed on Sep. 25, 2018, which is a division of U.S. patentapplication Ser. No. 14/643,253 filed on Mar. 10, 2015, now U.S. Pat.No. 10,114,195 issued on Oct. 30, 2018, and claims the benefit under 35USC 119(a) of Korean Patent Application No. 10-2014-0139756 filed onOct. 16, 2014, in the Korean Intellectual Property Office, the entiredisclosures of which are incorporated herein by reference for allpurposes.

BACKGROUND

The present disclosure relates to an optical system.

Recently, mobile communications terminals have been provided with cameramodules, so that video calls, as well as the capturing of still andmoving images, are possible. In addition, as the functionality ofcameras included in mobile communications terminals has graduallyincreased, cameras for mobile communications terminals have come to berequired to have high levels of resolution and high degrees ofperformance.

However, in accordance with the trend for the gradual miniaturizationand lightening of mobile communications terminals, there are limitationsin implementing cameras having levels of resolution and high degrees ofperformance.

In order to solve such problems, recently, the lenses included in cameramodules have been formed of plastic, a material lighter than glass, anda lens module has been configured using five or more lenses in order toimplement a high level of resolution therein.

SUMMARY

An aspect of the present disclosure may provide an optical systemcapable of improving an aberration improvement effect and implementinghigh resolution.

According to an aspect of the present disclosure, an optical system mayinclude: a first lens having negative refractive power and having twoconcave surfaces; a second lens having positive refractive power; athird lens having refractive power; a fourth lens having refractivepower; a fifth lens having refractive power; a sixth lens havingrefractive power; and a seventh lens having refractive power, whereinthe first to seventh lenses are sequentially disposed from an objectside, whereby an aberration improvement effect may be increased and highresolution and a wide angle may be implemented.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features and other advantages of thepresent disclosure will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

FIG. 1 is a configuration diagram of an optical system according to afirst exemplary embodiment of the present disclosure.

FIGS. 2 and 3 are curves showing aberration characteristics of theoptical system shown in FIG. 1.

FIG. 4 is a table showing characteristics of each lens of the opticalsystem shown in FIG. 1.

FIG. 5 is a table showing aspherical surface coefficients of each lensof the optical system shown in FIG. 1.

FIG. 6 is a configuration diagram of an optical system according to asecond exemplary embodiment of the present disclosure.

FIGS. 7 and 8 are curves showing aberration characteristics of theoptical system shown in FIG. 6.

FIG. 9 is a table showing characteristics of each lens of the opticalsystem shown in FIG. 6.

FIG. 10 is a table showing aspherical surface coefficients of each lensof the optical system shown in FIG. 6.

FIG. 11 is a configuration diagram of an optical system according to athird exemplary embodiment of the present disclosure.

FIGS. 12 and 13 are curves showing aberration characteristics of theoptical system shown in FIG. 11.

FIG. 14 is a table showing characteristics of each lens of the opticalsystem shown in FIG. 11.

FIG. 15 is a table showing aspherical surface coefficients of each lensof the optical system shown in FIG. 11.

DETAILED DESCRIPTION

Exemplary embodiments of the present disclosure will now be described indetail with reference to the accompanying drawings.

The disclosure may, however, be embodied in many different forms andshould not be construed as being limited to the embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of thedisclosure to those skilled in the art.

In the drawings, the shapes and dimensions of elements may beexaggerated for clarity, and the same reference numerals will be usedthroughout to designate the same or like elements.

In the following lens configuration diagrams, thicknesses, sizes, andshapes of lenses have been slightly exaggerated for explanation.Particularly, a shape of a spherical surface or an aspherical surfaceshown in the lens configuration diagrams has been shown only by way ofexample. That is, the spherical surface or the aspherical surface is notlimited to having the shown shape.

In addition, it is to be noted that a first lens refers to a lens thatis the closest to an object side, and a seventh lens refers to a lensthat is the closest to an image side.

Further, it is to be noted that the term ‘front’ refers to a directionfrom the optical system toward the object side, while the term ‘rear’refers to a direction from the optical system toward an image sensor orthe image side. Further, it is to be noted that a first surface of eachlens refers to a surface close to the object side (or an object-sidesurface) and a second surface of each lens refers to a surface close tothe image side (or an image-side surface). Further, in the presentspecification, it is to be noted that units of all of numerical valuesof radii of curvature, thicknesses, and the like, of lenses are mm.

An optical system according to an exemplary embodiment of the presentdisclosure may include seven lenses.

That is, the optical system according to an exemplary embodiment of thepresent disclosure may include a first lens, a second lens, a thirdlens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens.

However, the optical system according to an exemplary embodiment of thepresent disclosure is not limited to including only the seven lenses,but may further include other components, if necessary. For example, theoptical system may further include a stop controlling an amount oflight. In addition, the optical system may further include an infraredcut-off filter cutting off an infrared ray. Further, the optical systemmay further include an image sensor converting an image of a subjectincident thereto into an electrical signal. Further, the optical systemmay further include a gap maintaining member adjusting a gap betweenlenses.

The first to seventh lenses configuring the optical system according toan exemplary embodiment of the present disclosure may be formed of glassor plastic.

For example, the fourth to seventh lenses may be formed of the plastic,and the first to third lenses may be formed of the glass or the plastic.

In addition, at least one of the first to seventh lenses may have anaspherical surface. Further, each of the first to seventh lenses mayhave at least one aspherical surface.

That is, at least one of first and second surfaces of the first toseventh lenses may be aspherical. Here, the aspherical surfaces of thefirst to seventh lenses may be represented by Equation 1 below.

$\begin{matrix}{Z = {\frac{{cY}^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)c^{2}Y^{2}}}} + {AY}^{4} + {BY}^{6} + {CY}^{8} + {DY}^{10} + {EY}^{12} + {FY}^{14} + \ldots}} & (1)\end{matrix}$

Here, c is a curvature (an inverse value of a radius of curvature) at anapex of the lens, K is a conic constant, and Y is a distance in adirection perpendicular to an optical axis. In addition, constants A toF mean aspherical surface coefficients. In addition, Z indicates adistance from the apex of the lens in an optical axis direction.

The optical system including the first to seventh lenses may havenegative refractive power/positive refractive power/positive refractivepower/positive refractive power/negative refractive power/positiverefractive power/positive or negative refractive power sequentially fromthe object side.

The optical system configured as described above may improve opticalperformance through aberration improvement.

The optical system according to an exemplary embodiment of the presentdisclosure may satisfy Conditional Expression 1 below.

ANG≥90°  (Conditional Expression 1)

Here, ANG is a field of view of the optical system.

The optical system according to an exemplary embodiment of the presentdisclosure may satisfy Conditional Expression 2 below.

53°<ANG/Fno<61°  (Conditional Expression 2)

Here, ANG is the field of view of the optical system, and Fno is aconstant indicating brightness of the optical system.

The optical system according to an exemplary embodiment of the presentdisclosure may satisfy Conditional Expression 3 below.

Fno≤1.7  (Conditional Expression 3)

Here, Fno is the constant indicating the brightness of the opticalsystem.

The optical system according to an exemplary embodiment of the presentdisclosure may satisfy Conditional Expression 4 below.

Fno≤1.6  (Conditional Expression 4)

Here, Fno is the constant indicating the brightness of the opticalsystem.

The optical system according to an exemplary embodiment of the presentdisclosure may satisfy Conditional Expression 5 below.

1.6<ImgH/EPD<1.8  (Conditional Expression 5)

Here, ImgH is one-half of a diagonal length of an imaging surface of theimage sensor, and EPD is an entrance pupil diameter of the opticalsystem. Here, an entrance pupil means an image by a lens positioned infront of the stop.

The optical system according to an exemplary embodiment of the presentdisclosure may satisfy Conditional Expression 6 below.

3.7<TTL/EFL<4.0  (Conditional Expression 6)

Here, TTL is a distance from an object-side surface of the first lens tothe imaging surface of the image sensor, and EFL is an overall focallength of the optical system.

The optical system according to an exemplary embodiment of the presentdisclosure may satisfy Conditional Expression 7 below.

17°<ANG/TTL<20°  (Conditional Expression 7)

Here, ANG is the field of view of the optical system, and TTL is thedistance from the object-side surface of the first lens to the imagingsurface of the image sensor.

The optical system according to an exemplary embodiment of the presentdisclosure may satisfy Conditional Expression 8 below.

3.5<TTL/ImgH<3.8  (Conditional Expression 8)

Here, TTL is the distance from the object-side surface of the first lensto the imaging surface of the image sensor, and ImgH is one-half of thediagonal length of the imaging surface of the image sensor.

The optical system according to an exemplary embodiment of the presentdisclosure may satisfy Conditional Expression 9 below.

0.4<SL/TTL<0.55  (Conditional Expression 9)

Here, SL is a distance from the stop to the imaging surface of the imagesensor, and TTL is the distance from the object-side surface of thefirst lens to the imaging surface of the image sensor.

Next, the first to seventh lenses configuring the optical systemaccording to an exemplary embodiment of the present disclosure will bedescribed.

The first lens may have negative refractive power. In addition, bothsurfaces of the first lens may be concave. In detail, a first surface ofthe first lens may be concave toward an object, and a second surfacethereof may be concave toward an image.

At least one of the first and second surfaces of the first lens may beaspherical. For example, both surfaces of the first lens may beaspherical.

The second lens may have positive refractive power. In addition, bothsurfaces of the second lens may be convex.

At least one of first and second surfaces of the second lens may beaspherical. For example, both surfaces of the second lens may beaspherical.

The third lens may have positive refractive power. In addition, thethird lens may have a meniscus shape in which it is convex toward theobject. In detail, first and second surfaces of the third lens may beconvex toward the object.

At least one of the first and second surfaces of the third lens may beaspherical. For example, both surfaces of the third lens may beaspherical.

The fourth lens may have positive refractive power. In addition, bothsurfaces of the fourth lens may be convex.

At least one of first and second surfaces of the fourth lens may beaspherical. For example, both surfaces of the fourth lens may beaspherical.

The fifth lens may have negative refractive power. In addition, bothsurfaces of the fifth lens may be concave. In detail, a first surface ofthe fifth lens may be concave toward the object, and a second surfacethereof may be concave toward the image.

In addition, the fifth lens may have a meniscus shape in which it isconvex toward the image. In detail, the first and second surfaces of thefifth lens may be convex toward the image.

At least one of the first and second surfaces of the fifth lens may beaspherical. For example, both surfaces of the fifth lens may beaspherical.

The sixth lens may have positive refractive power. In addition, bothsurfaces of the sixth lens may be convex.

At least one of first and second surfaces of the sixth lens may beaspherical. For example, both surfaces of the sixth lens may beaspherical.

The seventh lens may have negative refractive power. In addition, theseventh lens may have a meniscus shape in which it is convex toward theobject. In detail, first and second surfaces of the seventh lens may beconvex toward the object.

In addition, the seventh lens may have an inflection point formed on atleast any one of the first and second surfaces thereof. For example, thesecond surface of the seventh lens may be concave in a paraxial regionand become convex toward an edge thereof.

In addition, at least one of the first and second surfaces of theseventh lens may be aspherical. For example, both surfaces of theseventh lens may be aspherical.

In the optical system configured as described above, a plurality oflenses perform an aberration correction function, whereby aberrationimprovement performance may be improved. In addition, in the opticalsystem, the first lens may have the negative refractive power toimplement a wide field of view, and the second lens may have thepositive refractive power to smoothly correct spherical aberration.

In addition, the third lens may have the positive refractive power tofurther smoothly correct spherical aberration and coma aberration.

An optical system according to a first exemplary embodiment of thepresent disclosure will be described with reference to FIGS. 1 through5.

The optical system according to a first exemplary embodiment of thepresent disclosure may include a first lens 110, a second lens 120, athird lens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160,and a seventh lens 170, and may further include a stop ST, an infraredcut-off filter 180, and an image sensor 190.

Here, lens characteristics (radii of curvature, thicknesses of lenses ordistances between the lenses, refractive indices, and Abbe's numbers) ofeach lens are shown in FIG. 4.

In a first exemplary embodiment of the present disclosure, the firstlens 110 may have negative refractive power and have two concavesurfaces. The second lens 120 may have positive refractive power andhave both surfaces that are convex. The third lens 130 may have positiverefractive power and have a meniscus shape in which it is convex towardthe object. The fourth lens 140 may have positive refractive power andhave both surfaces that are convex. The fifth lens 150 may have negativerefractive power and have two concave surfaces. The sixth lens 160 mayhave positive refractive power and have both surfaces that are convex.The seventh lens 170 may have negative refractive power and have ameniscus shape in which it is convex toward the object. In addition, theseventh lens 170 may have an inflection point formed on at least one offirst and second surfaces thereof.

Meanwhile, the respective surfaces of the first to seventh lenses 110 to170 may have aspherical surface coefficients as shown in FIG. 5. Thatis, all of the first surface of the first lens 110 to the second surfaceof the seventh lens 170 may be aspherical.

In addition, the stop ST may be disposed between the fourth lens 140 andthe fifth lens 150.

In addition, the first lens 110 among the first to seventh lenses 110 to170 may have the largest effective radius, and the second lens 120 amongthe first to seventh lenses 110 to 170 may have the second largesteffective radius.

In addition, the optical system configured as described above may haveaberration characteristics shown in FIGS. 2 and 3.

Meanwhile, it may be appreciated from Table 1 that an optical systemaccording to a first exemplary embodiment of the present disclosuresatisfies Conditional Equations 1 to 9 described above. Therefore,optical performance of the lens may be improved.

TABLE 1 EFL 1.31 Fno 1.6841 ANG 90.00° EPD 0.78 TTL 5.01 SL 2.40 ImgH1.34 ANG/Fno 53.44°

An optical system according to a second exemplary embodiment of thepresent disclosure will be described with reference to FIGS. 6 through10.

The optical system according to a second exemplary embodiment of thepresent disclosure may include a first lens 210, a second lens 220, athird lens 230, a fourth lens 240, a fifth lens 250, a sixth lens 260,and a seventh lens 270, and may further include a stop ST, an infraredcut-off filter 280, and an image sensor 290.

Here, lens characteristics (radii of curvature, thicknesses of lenses ordistances between the lenses, refractive indices, and Abbe's numbers) ofeach lens are shown in FIG. 9.

In a second exemplary embodiment of the present disclosure, the firstlens 210 may have negative refractive power and have two concavesurfaces. The second lens 220 may have positive refractive power andhave both surfaces that are convex. The third lens 230 may have positiverefractive power and have a meniscus shape in which it is convex towardthe object. The fourth lens 240 may have positive refractive power andhave both surfaces that are convex. The fifth lens 250 may have negativerefractive power and have a meniscus shape in which it is convex towardthe image. The sixth lens 260 may have positive refractive power andhave both surfaces that are convex. The seventh lens 270 may havenegative refractive power and have a meniscus shape in which it isconvex toward the object. In addition, the seventh lens 270 may have aninflection point formed on at least one of first and second surfacesthereof.

Meanwhile, the respective surfaces of the first to seventh lenses 210 to270 may have aspherical surface coefficients as shown in FIG. 10. Thatis, all of the first surface of the first lens 210 to the second surfaceof the seventh lens 270 may be aspherical.

In addition, the stop ST may be disposed between the fourth lens 240 andthe fifth lens 250.

In addition, the first lens 210 among the first to seventh lenses 210 to270 may have the largest effective radius, and the second lens 220 amongthe first to seventh lenses 210 to 270 may have the second largesteffective radius.

In addition, the optical system configured as described above may haveaberration characteristics shown in FIGS. 7 and 8.

Meanwhile, it may be appreciated from Table 2 that an optical systemaccording to a second exemplary embodiment of the present disclosuresatisfies Conditional Equations 1 to 9 described above. Therefore,optical performance of the lens may be improved.

TABLE 2 EFL 1.29 Fno 1.5881 ANG 90.00° EPD 0.81 TTL 4.80 SL 2.53 ImgH1.32 ANG/Fno 56.67°

An optical system according to a third exemplary embodiment of thepresent disclosure will be described with reference to FIGS. 11 through15.

The optical system according to a third exemplary embodiment of thepresent disclosure may include a first lens 310, a second lens 320, athird lens 330, a fourth lens 340, a fifth lens 350, a sixth lens 360,and a seventh lens 370, and may further include a stop ST, an infraredcut-off filter 380, and an image sensor 390.

Here, lens characteristics (radii of curvature, thicknesses of lenses ordistances between the lenses, refractive indices, and Abbe's numbers) ofeach lens are shown in FIG. 14.

In a third exemplary embodiment of the present disclosure, the firstlens 310 may have negative refractive power and have two concavesurfaces. The second lens 320 may have positive refractive power andhave both surfaces that are convex. The third lens 330 may have positiverefractive power and have a meniscus shape in which it is convex towardthe object. The fourth lens 340 may have positive refractive power andhave both surfaces that are convex. The fifth lens 350 may have negativerefractive power and have a meniscus shape in which it is convex towardthe image. The sixth lens 360 may have positive refractive power andhave both surfaces that are convex. The seventh lens 370 may havenegative refractive power and have a meniscus shape in which it isconvex toward the object. In addition, the seventh lens 370 may have aninflection point formed on at least one of first and second surfacesthereof.

Meanwhile, the respective surfaces of the first to seventh lenses 310 to370 may have aspherical surface coefficients as shown in FIG. 15. Thatis, all of the first surface of the first lens 310 to the second surfaceof the seventh lens 370 may be aspherical.

In addition, the stop ST may be disposed between the fourth lens 340 andthe fifth lens 350.

In addition, the first lens 310 among the first to seventh lenses 310 to370 may have the largest effective radius, and the second lens 320 amongthe first to seventh lenses 310 to 370 may have the second largesteffective radius.

In addition, the optical system configured as described above may haveaberration characteristics shown in FIGS. 11 and 12.

Meanwhile, it may be appreciated from Table 3 that an optical systemaccording to a third exemplary embodiment of the present disclosuresatisfies Conditional Equations 1 to 9 described above. Therefore,optical performance of the lens may be improved.

TABLE 3 EFL 1.23 Fno 1.5532 ANG 94.00° EPD 0.79 TTL 4.80 SL 2.52 ImgH1.34 ANG/Fno 60.52°

As set forth above, with the optical system according to exemplaryembodiments of the present disclosure, an aberration improvement effectmay be increased, and high resolution and a wide angle may beimplemented.

While exemplary embodiments have been shown and described above, it willbe apparent to those skilled in the art that modifications andvariations could be made without departing from the scope of the presentinvention as defined by the appended claims.

What is claimed is:
 1. An optical system comprising: a first lens havinga negative refractive power; a second lens having a positive refractivepower; a third lens having a positive refractive power; a fourth lenshaving a refractive power; a fifth lens having a negative refractivepower; a sixth lens having a positive refractive power; and a seventhlens having a negative refractive power, wherein the first to seventhlenses are sequentially disposed from an object side of the opticalsystem toward an image side of the optical system, and 53°<ANG/Fno<61°is satisfied, where ANG is a field of view of the optical system and Fnois a constant indicating a brightness of the optical system.
 2. Theoptical system of claim 1, wherein ANG 90° is satisfied.
 3. The opticalsystem of claim 1, wherein the first lens has a concave object-sidesurface.
 4. The optical system of claim 1, wherein the second lens has aconvex object-side surface.
 5. The optical system of claim 1, whereinthe third lens has a convex object-side surface.
 6. The optical systemof claim 1, wherein the fourth lens has a convex image-side surface. 7.The optical system of claim 1, wherein the fifth lens has a concaveobject-side surface.
 8. The optical system of claim 1, wherein the fifthlens has a meniscus shape in which an object-side surface of the fifthlens is concave and an image-side surface of the fifth lens is convex.9. The optical system of claim 1, wherein the sixth lens has a convexobject-side surface and a convex image-side surface.
 10. The opticalsystem of claim 1, wherein the seventh lens has a meniscus shape inwhich an object-side surface of the seventh lens is convex and animage-side surface of the seventh lens is concave.
 11. The opticalsystem of claim 1, wherein the seventh lens has an inflection pointformed on either one or both of an object-side surface of the seventhlens and an image-side surface of the seventh lens.
 12. The opticalsystem of claim 1, wherein an object-side surface and an image-sidesurface of each of the first to seventh lenses are aspherical.